The growth of digital communications has created an increased demand for broadband communications infrastructure. A significant component of the cost of creating this infrastructure is the cost of providing fixed cabling in the Customer Access Network (“CAN”). A method of reducing the cost of a broadband CAN is to use fixed broadband wireless to provide communication links between subscribers and a fixed backbone network.
The Broadband Wireless Internet Forum (“BWIF”) has created a standard for the provision of fixed broadband wireless. The standard involves the use of a Wireless Access Termination System (“WATS”) to broadcast information to a group of subscribers on a downstream channel. The subscribers send information to the WATS using a shared upstream channel. Each subscriber is allocated access to a channel in accordance with a Medium Access Protocol (“MAC”).
A limitation of the BWIF specification is that the subscribers communicate on the upstream channel using the same modulation and encoding schemes. The characteristics of the upstream channel can vary depending on the location of an individual subscriber. Therefore, use of a modulation and encoding scheme that is appropriate for certain channel conditions can unnecessarily impact on the Quality of Service (“QoS”) experienced by individual subscribers. If a modulation scheme is chosen to provide high throughput in a channel with high Signal to Interference plus Noise Ratio (“SINR”), then subscribers in locations where the upstream channel has a low SINR will experience very high Bit Error Rates (“BER”). Alternatively, if a modulation scheme is chosen to provide low BERs in a channel with a low SINR, then subscribers in locations where the upstream channel has a high SINR can experience sub-optimal throughput. This problem can be overcome by allowing individual subscribers to transmit using a modulation scheme that continually adapts to the channel conditions experienced by the subscriber in order to provide near optimal throughput for those channel conditions.